Stabilized sodium carbonate peroxyhydrate

ABSTRACT

The invention relates to a stable sodium carbonate peroxyhydrate which is suited for use together with crystalline synthetic silicate-based detergents and is coated with an alkali metal sulfate and a copolymer or terpolymer of vinyl pyrrolidone.

The invention relates to a stabilized sodium carbonate peroxyhydratesuited for use together with crystalline synthetic silicate-baseddetergent powders.

Sodium perborate has long been used as a bleaching agent in laundrydetergents.

The principal commercial product was sodium perborate tetrahydrate(PB4). The drawback of PB4 is its poor solubility in water. When lowertemperatures and the use of hydrogen peroxide activators such as TAEDwere adopted in the washing of laundry, a shift was made in laundrydetergents to the use of sodium perborate monohydrate (PB1), which has ahigher solubility. Subsequently the use of sodium perborate has alsobeen adopted in dishwashing machine detergents instead of chlorinecompounds and in stain remover salts.

Sodium perborate is a fairly economical product and relatively stable inphosphate-free detergents, which have become common especially incountries which do not have wide-scale and efficient treatment of wastewaters. Perhaps the biggest drawback of sodium perborate is that itcontains boron. It has been presumed that boron causes health risks andtherefore, for example, maximum limits have been set for the amount ofboron in drinking water, and in many places these limitations are beingmade stricter. For this reason there is need for a boron-free bleachingagent which is not hazardous to watercourses or to human beings. Also,the solubility of sodium perborate is not optimal for all products.

Sodium carbonate peroxyhydrate (2Na₂CO₃*3H₂O₂) would theoretically be arelatively desirable product, since environmentally non-desirabledegradation products are not produced from this bleaching agent. Inaddition, its solubility is quite good. Sodium carbonate peroxyhydrateis commonly referred to with the erroneous name of “sodiumpercarbonate,” suggesting that the compound in question is a so-calledper-compound or per-salt. As the formula presented above shows, sodiumcarbonate peroxyhydrate is merely a so-called addition product, in whichthe hydrogen peroxide is quite loosely bonded, and it contains no groupcorresponding to the structure of actual per-compounds, as do, forexample, sodium perborate. sodium monopersulfate, alkali persulfates,etc. A real sodium percarbonate does exist, but it is a hazardousproduct which cannot be used in household products. Evidently owingpartly to its addition structure, sodium carbonate peroxyhydrate is notvery stable, and therefore high technical requirements are set for aprocess for the production of sodium carbonate peroxyhydrate.

In technochemical household products, for example, in dishwashingmachine detergents and in stain removers the properties of which areincreasingly beginning to approach those of actual detergents so thatthey contain, among other ingredients, tensides, enzymes, hydrogenperoxide activators, etc., it is desirable to protect sodium carbonateperoxyhydrate from decomposition.

Bleaching agents are used in technochemical household products mostly inlaundry detergents. In laundry detergents, silicate-based products suchas zeolites, in particular zeolite 4A, are being used increasinglyinstead of phosphates as so-called builders. It has not been possible touse sodium carbonate peroxyhydrate in zeolite-containing detergentsbecause the product decomposes very rapidly upon coming into contactwith zeolite. The reason for this is not precisely known. It must betaken into account that zeolites normally contain quite considerableamounts of water, for example zeolite 4A usually contains water approx.20%.

In order to give a washing powder an environment-friendly image, zeoliteis being used increasingly as a builder instead of phosphate. At thesame time, the aim has been to shift to the use of sodium carbonateperoxyhydrate instead of sodium perborate. In this case, problems havebeen encountered owing to the instability of sodium carbonateperoxyhydrate. A large number of stabilization methods have beendeveloped to solve this problem.

A considerable number of inventions relate to coatings which contain inthe coating layers boric acids or boron salts, such as ortho- andmetaborates. The use of additives such as silicates and magnesiumsulfate have also been proposed. EP applications 459 625 (Mitsubishi GasChem.) and 675 851 (Solvey Interox) propose the use of boric acid andsilicates as the coating; EP application 675 852 (Solvey Interox) boricacid and phosphates; EP application 487 256 (Kao Corp.) a borate; EPapplications 652 809 and 523 169 (FMC Corp.) borosilicate and phosphonicacid derivatives; and U.S. Pat. No. 4,526,698 (Kao Corp.) a borate andan alkali metal silicate or a Mg compound.

All of such methods have the disadvantage that, even though thestability is relatively good, boron has not been entirely eliminated.Furthermore, the solubility of sodium carbonate peroxyhydrate is oftendecreased, which is not necessarily good. Combinations of sodium sulfateand sodium chloride have also been used for coating sodium carbonateperoxyhydrate, for example, in EP applications 592 969 and 624 549(Solvey Interox). In these methods, stability may be based on the factthat sodium sulfate, sodium chloride and sodium carbonate which may formupon the degradation of sodium carbonate peroxyhydrate are known to forman addition product together with hydrogen peroxide. There is thedisadvantage that chloride, as is known, causes corrosion of stainlesssteel appliances, such as household appliances. The amounts of coatingmust also be rather large. Furthermore, chlorinated products may beformed in a reaction between the organic ingredients of detergents,hydrogen peroxide or its degradation products and chloride.

The use of inorganic salts in a coating, together with special coatingtechniques, also seems to be the most common method of attempting toimprove the stability of sodium carbonate peroxyhydrate.

Another group consists of coating methods based on the use of organicsubstances, either monomeric or polymeric.

The applicant's patent application WO-94/05594 describes a method bywhich a product quite stable as such is obtained. The product is highlysuitable for, for example, stain removers in which sodium carbonateperoxyhydrate is used as such or for products in which relatively inertsubstances such as pure sodium carbonate and possibly only small amountsof ordinary detergent components are added to the said chemical.

JP application 61 36216 (Sunstar INC. et al.) describes a cleansingagent for dentures, which contains glauber salt 17% and a per-compound,e.g. sodium percarbonate. Glauber salt is a hydrous form of sodiumsulfate, sodium sulfate decahydrate. Sodium percarbonate is first mixedwith glauber salt, thereafter a polymer in an alcohol solution isatomized over the mixture, which polymer may be, for example, polyvinylpyrrolidone, and the alcohol is evaporated. The product thus obtained isthen mixed with the other components of the cleansing agent to obtainthe final cleansing agent for dentures.

JP application 60 30723 (Matsamura Kagaku Kogyo) discloses a product forcleaning urine-stained textiles. Sodium carbonate peroxyhydrate andcertain actual peroxy compounds, such as potassium percarbonate andcertain persulfates and perborate, are coated by sprinklingwater-soluble non-heavy metal salt powders, such as sulfates, chloridesand phosphates, over the said hydrogen peroxide compounds orper-compounds and by using a water-soluble adhesive such as polyvinylpyrrolidone and other water-soluble polymers which contain, amongothers, maleate and acrylate groups, in order to obtain the finalproduct. It is difficult by means of powder sprinkling to render thesurface of sodium carbonate peroxyhydrate sufficiently protective inorder that the product could be used in detergents and in particulardetergents which contain zeolite, which very rapidly decomposes sodiumcarbonate peroxyhydrate. At least the amounts of material used for thepowder sprinkling must be quite large. Indeed, in the invention aninorganic salt is used in an amount of 20-35% in proportion to theinorganic peroxy salt.

The present applicant has developed a method (FI-patent application935342) in which a very good stability is achieved with a sodium sulfatecoating in, for example, a carbon dioxide atmosphere, when the productis tested in a mixture with zeolite. The method has the drawback thatusually a rather large amount of sodium sulfate is needed in order toachieve high stability in long-term tests and severe conditions. Theachieving of a high stability requires a sodium sulfate content ofapprox. 25%. In this case the active oxygen content of the product dropsfrom 13-14%, which is the practical value for sodium carbonateperoxyhydrate, to below 11%. In certain detergent applications this istoo low a value in order for the detergent to be optimally formulatedwithout its containing too much of a component containing a bleachingagent. For this reason it would be desirable to decrease the amount ofcoating.

It is an object of the present invention to provide a storage-stablesodium carbonate peroxyhydrate which, when coming into contact withsilicate-based detergents, remains undegraded for quite a long time. Itis also an object of the invention to make possible the production ofdetergent compositions the ingredients of which areenvironment-friendly.

These objects are achieved in accordance with the invention with astable sodium carbonate peroxyhydrate which is coated with an alkalimetal sulfate and a copolymer or terpolymer of vinylpyrrolidone.

The characteristics of the invention are stated in the accompanyingclaims 1-16.

It was observed, surprisingly, that, by using certain copolymers orterpolymers of vinyl pyrrolidone together with an alkali metal sulfatefor coating sodium carbonate peroxyhydrate, a very stable product wasobtained which is suitable for use with silicate-based detergents, suchas zeolites and sheet silicates. Furthermore, it was observed that inorder to achieve the same stability as has a product coated with sodiumsulfate alone, the use of copolymers or terpolymers makes it possible todecrease the amount of sodium sulfate. Thereby the active oxygen contentof sodium carbonate peroxyhydrate is retained and optimal formulation indetergent applications is facilitated, since bleaching agent need not beused in excessive amounts.

The coating can be carried out by known procedures, preferably by thefluidization technique, wherein sodium sulfate and thepolymer-containing solution according to the invention are atomized intoa fluid-bed drier in a selected order. The atomization may also becarried out so that the polymer and the sodium sulfate are mixedtogether to form a solution. Often in such a case the dissolving musttake place immediately before the atomization in order that noprecipitation should occur. The coating can also be carried out bykneading the sodium carbonate peroxyhydrate in the said mixture. This isvery economical if the sodium carbonate used as the initial substance isfinely divided, in which case an increase of the particle size is alsoachieved by granulation.

Since sodium carbonate peroxyhydrate is an alkaline product which iscatalyzed by all heavy-metal ions, their hydroxides, oxides andoxyhydroxides, it is clear that stabilization can be improved by usingknown chelators of metals, such as phosphonic acid derivatives,aminopolycarboxylic acids, antioxidants, etc., which are used forstabilizing hydrogen peroxide in alkaline conditions.

Polymers according to the invention can be used advantageously in boththe intermediate layer and the surface layer, i.e. the sodium sulfatemay be added after the polymer treatment or before it In this case theuse of blends of polymers and sodium sulfate is also possible.

The polymers usable for coating in accordance with the invention includethe copolymers and terpolymers of vinyl pyrrolidone. The copolymer orterpolymer is formed by polymerizing together N-vinyl pyrrolidone and amonomer which contains at least one vinyl group.

The monomer which contains a vinyl group may be an a-olefin whichcontains 2-20 carbon atoms, an aromatic monomer, an ester monomer, anester monomer derivative, a (meth)acrylic acid derivative or aheterocyclic monomer. The α-olefin may be, for example, ethylene,propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene,1-hexadecene or 1-eicocene. The aromatic monomer may be a styrene or amethyl styrene. The ester monomer may be, for example, selected from thegroup consisting of vinyl acetate, (meth)acrylic acid N-alkyl-aminoalkylester, or a quaternized salt of these. The (meth)acrylic acid derivativemay be, for example, a (meth)acrylic acid amide derivative. Theheterocyclic monomer may be, for example, vinyl caprolactame. Theterpolymer may be formed, for example, by polymerizing together N-vinylpyrrolidone, vinyl caprolactame and dimethylaminoethyl (meth)acrylatemonomer. Preferred polymers include N-vinyl pyrrolidone 1-butylcopolymer or N-vinyl pyrrolidone 1-hexadecane copolymer. Copolymerswhich have been formed by polymerizing N-vinyl pyrrolidone with styrene,methyl styrene, vinyl acetate, di-(1-3 carbon atom)alkylamino-(2-6carbon atom)alkyl (meth)acrylate, vinyl caprolactame or (meth)acrylicacid amide derivative, such as (3-(methacryloylamino)propyl)trimethylammonium chloride.

It is also possible to use homopolymers of vinyl pyrrolidone, such aspolyvinyl pyrrolidone (PVP), as an additive in the coating of sodiumcarbonate peroxyhydrate.

However, such additives do not provide any significant advantages oversodium sulfate alone when coated sodium carbonate peroxyhydrates aretested in a blend with silicate-based detergents. The products are,however, well suited for blends in which a silicate-based detergent isnot used as a blend component, such as stain remover salts.

The sodium carbonate peroxyhydrate according to the invention,containing sodium sulfate and a polymer, is suitable for use withsilicate-based detergent powders, such as zeolites and sheet silicates.

The use of coatings is not limited only to products containing zeolite4A. It is known that, for example, zeolite 24A contains less water thandoes zeolite 4A, and sodium carbonate peroxyhydrate decomposes moreslowly in contact with zeolite 24A than with zeolite 4A. In productswhich contain zeolite 24A (Crosfield Group) it is also possible to usecoatings according to the invention to improve further the stability ofsodium carbonate peroxyhydrate. The coatings according to the inventionare also suitable for products which contain so-called sheet silicates,which are produced by, for example, Hoechst AG.

It has been presumed that the decomposition of sodium carbonateperoxyhydrate is due to the effect of water. This water may be derivedfrom outside or from the decomposition of the product. The hypothesishas been that such water must be bonded if it is formed between thepercarbonate and the coating, or it is necessary to prevent its accessto dissolve the product, whereupon hydrogen peroxide is released andpasses into the alkaline solution, in which hydrogen peroxide is knownto decompose rapidly and especially if there are present heavy metalions, their hydroxides, oxides or oxyhydroxides. As regards zeolites, ahypothesis is that zeolite 4A normally contains adsorbed water approx.20%. This water may “dissolve” sodium carbonate peroxyhydrate, whereuponthe hydrogen peroxide passes into an alkaline solution, in whichhydrogen peroxide is known to be instable, especially in the presence ofheavy metal ions and their hydroxides, oxides or oxyhydroxides. Anotherhypothesis is that hydrogen peroxide is very apt to change places withthe water present in zeolite. Thereupon, hydrogen peroxide woulddecompose quite easily.

In the product according to the invention it is surprising that the mosthygroscopic polymers usually worked best and, in turn, those productsthe water adsorption capacity of which is lowest, but by no means zero,yielded poorer results. Thus, for example, the water present in zeolitemay not as such be the crucial factor in the decomposition process; thedecomposition must to a considerable degree be due to other factors. Itis known that at an elevated temperature an adduct of hydrogen peroxidecan be prepared from polyvinyl pyrrolidone at an elevated temperature.One hypothesis could be that the products in question would form anadduct preventing the decomposition of hydrogen peroxide as hydrogenperoxide is released under the effect of water.

It may also be that a perhydroxyl anion which forms especially rapidlyfrom hydrogen peroxide in alkaline conditions becomes in some mannerbonded to the nitrogen group, or that a hydroxyl radical which formsfrom the perhydroxyl anion and may promote a chain reaction reacts withthe polymer concerned and at the same time becomes inactive. This wouldbe supported by the fact that polyvinyl pyrrolidone contains tertiarynitrogen, which may in part stabilize the alkaline decomposition processof hydrogen peroxide. Thus a good additive must be sufficientlyhygroscopic, but it must not moisten the product and it must react withhydrogen peroxide or the products of further reactions thereof.

EXAMPLES

In all of the coating tests of examples 1-5, the material which wascoated was a sodium carbonate peroxyhydrate (NPH) having an activeoxygen content of 14.3% as measured by conventional potassiumpermanganate titration.

For the measuring of NPH stability there is commonly used a method inwhich the product is packed into a tightly closed cardboard case, andthus the method should illustrate the behavior of the product in anunopened consumer package. Such a package is then placed in a climatechamber the temperature and relative humidity of which are set atcertain values, for example, 30° C. and a relative humidity of 70%. Ifthe product is somehow stable, obtaining sufficient information aboutthe stability of the product would require long periods. Furthermore,the method does not provide information of how the product behaves whenthe package has been opened and it comes into contact with air. Anothermethod used is to place the product in a container which is closed withslightly permeable plastic film or a perforated film. This does notalways provide reliable results, either, since the oxygen formed uponthe decomposition of NPH is capable, at least in part, of preventing theambient air from coming into contact with the product. The samedifficulties are encountered when the product is tested in plastic bagswhich are not completely airtight.

The applicant has used a method which has worked well in the applicantstests and which yields reliable results regarding the behavior of theproduct already after a test period of one week. Two-week tests alreadyyield very reliable results. The test conditions are, however, quitesevere, since the products are tested in an open vessel at a temperatureof 30° C. and a relative humidity of 70%.

It has been observed previously that, for example zeolites very rapidlydecompose sodium carbonate peroxyhydrate. In the present invention, amethod was used in which NPH is mixed at a ratio of 1:1 with acommercial finely-divided zeolite 4A having a particle size of approx.10 microns. Such a blend is tested under the same conditions as weredescribed above.

The method is overall as follows: If the question is of pure NPH,precisely approx. 4-5 g of NPH is weighed into an open, flat-bottomedglass vessel having edges and a capacity of 15 ml. This vessel is placedin a climate chamber with the conditions stated above. After apredetermined period the vessel is taken out of the climate chamber. Thecontents and the hydrogen peroxide concentration are determined by aknown potassium permanganate method. If the effect of zeolite is beingexamined, NPH is mixed well with an equal amount by weight of acommercial zeolite 4A, in total 4-5 grams.

Example 1

Table 1 shows the stability of NPH alone and mixed with zeolite.

TABLE 1 Decrease of the active oxygen content of NPH alone and in ablend with zeolite, measured in percentages Product/time/decomposition %1 week 2 weeks 3 weeks 4 weeks NPH  5.7  7.0  8.7 10.4 NPH + zeolite44.0 65.5 80.0 87.0

It can be observed from the results that the stability of NPH is stillquite good after two weeks, but in a mixture with zeolite its stabilityis very poor.

Example 2

Table 2 shows the decomposition results, at different sodium sulfateconcentrations, of NPH samples coated by the method described in theapplicant's FI application 935342.

TABLE 2 Decomposition of NPH samples coated with different sodiumsulfate concentrations in a mixture with zeolite 4A in 2-week testsProduct/NAS content/decomposition % 25% 20% 15% 10% 5% NPH + zeolite14.3 16.0 17.8 20.8 25.0

NPHs coated in accordance with the invention are described in thefollowing examples:

Example 3

The coating tests were carried out by using an Aeromatic Strea 1apparatus. The polymers were dissolved in water to form saturatedsolutions of at maximum 10 percent concentration. An approx. 29 percentaqueous solution of sodium sulfate was used as the sodium sulfatesolution. The solutions were atomized in an elective order by means of a2-phase atomizer by using air as the atomization gas. The coatingamounts and thereby the coating thickness could be varied by changingthe solution amounts fed in.

If the sodium sulfate solution also contained a polymer solution, thissolution had to be atomized immediately in order to avoid precipitation,otherwise an uneven coating was formed.

When the objective was to produce a polymer-containing coating with asodium sulfate concentration of 20 percent, the following amounts ofmaterials were used:

300 g NPH

6 or 12 g polymer (concentration 1.6-3.1%) (recipes 1 and 2)

75 g sodium sulfate (NAS content 19.7-19.4%=approx. 20%)

When the polymer was fed in last, the polymer charge used was 15 g(3.8%), recipe 3.

By feeding in smaller amounts of solution, it was possible to reduce theamounts of sodium sulfate and polymer in the final coated product.

In the following test, the following homopolymers of vinyl pyrrolidonewere used:

K-30 of International Specialty Products (ISP), molecular weight 38,000

K-90 of ISP, molecular weight 630,000

PVP of Aldrich Chemicals, catalogue number 85, 654-2, molecular weight10,000, denoted in the table by PVP A.

TABLE 3 Comparative tests with NPH samples coated with approx. 20percent NAS and a polymer, decomposition percentage after 2 weeks in ablend with zeolite 4A Polymer used Recipe Decomposition K-30 1 15.3%K-30 2 20.8% K-30 3 13.3% K-90 1 15.4% K-90 2 18.8% K-90 3 22.7% PVP A 115.0% PVP A 2 19.6% PVP A 3 15.1%

Example 4

In the following tests, the following vinyl pyrrolidone polymers wereused:

Antara® 430=vinyl pyrrolidone—styrene copolymer (ISP product)

Antarons P 904 =butylpolyvinyl pyrrolidone (ISP product)

ACP =vinyl pyrtolidone acrylic acid (VP/AC) copolymer (ISP product)

ACP 1005 VP/AC 25:75, molecular weight high

ACP 1033 VP/AC 75:25, molecular weight average

ACP 1042 VP/AC 25:75, molecular weight average

The ACP products were the least hygroscopic of the polymers used in thetest.

TABLE 4 Results obtained with different products and recipes, the amountof NAS being approx. 20% Decomposition alone with zeolite Polymer Recipe2 weeks 2 weeks Antara ® 430 1 4.8%  8.5% Antaron ® P 904 1 4.0% 10.0% ″3 7.3%  9.8% ACP 1005 1 8.3% 22.8% ACP 1033 1 7.0% 39.8% ACP 1042 1 7.7%17.5%

Example 5

In the following series, the effect of the amounts of coating wasexamined, the amount of polymer being 1.6-2.0% (6 g) of the total endproduct amount.

TABLE 5 Effects of different amounts of coating Decomposition withzeolite Polymer NAS 2 weeks PVP A  0% 51.0% ″  5% 34.4% ″ 10% 25.0009% ″20% 16.7% Antara ® 430  0% 42.2% ″  5% 41.4% ″ 10% 12.5% ″ 20% 7.9%Antaron ® P 904  0% 45.8% ″  5% 33.6% ″ 10% 11.0% ″ 20% 6.0%

Example 6

In the following, the stability of poor-grade NPH was tested, the NPHbeing coated with a copolymer or terpolymer of vinyl pyrrolidonetogether with sodium sulfate. The product was contacted with zeolite(4A) at 30° C. and a relative humidity of 70%. The relativedecomposition percentages shown in the table were obtained through acomparison with NPH coated with only sodium sulfate in correspondingconditions.

TABLE 6 NPH stability tests NPH was coated with 10 per cent sodiumsulfate and polymer, decomposition in a blend with zeolite (50:50)during 2 weeks at 30° C. and a relative humidity of 70% coating %/coating %/ coating %/ coating %/ coating %/ Polymer/coating order/relative de- relative de- relative de- relative de- relative de-concentration/rela. composition composition composition compositioncomposition stability % % % % % 1. ANTARON P-904 PVP-NAS 1%/58.5%1.5%/48.8% NAS-PVP 1%/47.3% 1.5%/50.0% 2. ANTARON V-216 PVP-NAS 1%/53.3%3. ANTARA 430 PVP-NAS 1%/57.6% NAS-PVP 1%/61.3% 4. COPOLYMER 845 PVP-NAS1%/61.4% NAS-PVP 1%/69.5% 5. COPOLYMER 937 PVP-NAS 1%/61.8% NAS-PVP1%/58.3% 6. COPOLYMER 958 PVP-NAS 1%/58.6% NAS-PVP 1%/83.8% 7. H2OLDEP-1 PVP(10%)-NAS 1%/51.0% PVP(5%)-NAS 1%/40.6% NAS-PVP(10%) 1%/48.7%NAS-PVP(5%) 1%/49.0% 8. GAFQUAT HS-100 PVP-NAS 0.8%/46.0% 1.4%/47.8%NAS-PVP 0.8%/54.5% 1.5%/55.7% 9. GAFQUAT 734 PVP-NAS 1%/49.7% NAS-PVP1%/46.1% 10. GAFQUAT 755 N PVP-NAS 1%/53.9% NAS-PVP 1%/67.5% 11. PVP/VAW 735 PVP-NAS 0.5%/54.2% 1%/64.3% NAS-PVP 0.5%/48.4% 1%/71.7%

Products of International Specialty Products used in the table:

Antaron ® P-904 = Butylated PVP Antaron ® V-216 = PVP/hexadecenecopolymer Antara ® 430 = vinyl pyrrolidone/styrene copolymer PVP/VA 735W= poly(vinyl pyrrolidone/vinyl acetate copolymer) Copolymer 845 =poly(vinyl pyrrolidone/dimethylaminoethyl methacrylate) Copolymer 937 =poly(vinyl pyrrolidone/dimethylaminoethyl methacrylate) Copolymer 958 =poly(vinyl pyrrolidone/dimethylaminoethyl methacrylate) H₂OLD ® EP-1 =terpolymer of vinyl caprolactame, vinyl pyrrolidone anddimethylaminoethyl methacrylate Gafquat ® HS-100 = copolymer of vinylpyrrolidone and meth- acrylamidopropyltrimethyl ammonium chlorideGafquat ® 734 quaternized copolymer of vinyl pyrrolidone and 755 N = anddimethylaminoethyl methacrylate Other legend: PVP = copolymer orterpolymer of vinyl pyrrolidone PVP-NAS = coated first with PVP and thenwith sodium sulfate NAS-PVP = coated first with sodium sulfate and thenwith PVP PVP(X %) = an X per cent polymer solution used Coating % =proportion of polymer of the NPH amount Decomposition % = decompositionas a percentage of the decomposition of NPH coated with only sodiumsulfate

It can be seen that with the use of copolymers or terpolymers of vinylpyrrolidone in an amount of 0.5-1.5% (acronym PVP is used for thepolymers in the table even though the actual vinyl pyrrolidonehomopolymer, PVP, was not used) the decomposition of NPH is reduced to40-60% of what is achieved with only sodium sulfate coating.

What is claimed is:
 1. In a crystalline or synthetic silicate-baseddetergent composition, the improvement wherein the composition comprisesgranules of sodium carbonate peroxyhydrate coated with an alkali metalsulfate and a co-polymer or terpolymer of vinyl pyrrolidone.
 2. Thedetergent composition of claim 1 wherein the silicate component is azeolite.
 3. The detergent composition of claim 1 wherein the silicatecomponent is a sheet silicate.
 4. The detergent composition of claim 1wherein the alkali metal sulfate is sodium sulfate or potassium sulfate.5. The detergent composition of claim 1 wherein the copolymer orterpolymer is formed by polymerizing together N-vinyl pyrrolidone and amonomer which contains at least one vinyl group.
 6. The detergentcomposition of claim 1 wherein the copolymer is formed by polymerizingtogether N-vinyl pyrrolidone and an α-olefin monomer which contains 2-20carbon atoms.
 7. The detergent composition of claim 6 wherein theα-olefin which contains 2-20 carbon atoms is selected from the groupconsisting of ethylene, propylene, 1-butene, 1-pentene, 1-hexene,1-heptene, 1-octene, 1-decene, 1-hexadecene and 1 -eicocene.
 8. Thedetergent composition of claim 1 wherein the copolymer is a N-vinylpyrrolidone 1-butyl copolymer or a N-vinyl pyrrolidone 1-hexadecanecopolymer.
 9. The detergent composition of claim 1 wherein the copolymeris formed by polymerizing together N-vinyl pyrrolidone and an aromaticmonomer containing a vinyl group.
 10. The detergent composition of claim1 wherein the copolymer is formed by polymerizing together N-vinylpyrrolidone and an ester monomer containing a vinyl group.
 11. Thedetergent composition of claim 1 wherein the copolymer is formed bypolymerizing together N-vinyl pyrrolidone and an ester monomerderivative containing a vinyl group.
 12. The detergent composition ofclaim 1 wherein the copolymer is formed by polymerizing together N-vinylpyrrolidone and a (meth)acrylic acid amide derivative.
 13. The detergentcomposition of claim 1 wherein the copolymer is formed by polymerizingtogether N-vinyl pyirolidone and a heterocyclic monomer containing avinyl group.
 14. The detergent composition of claim 1 wherein theterpolymer is formed by polymerizing together N-vinyl pyrrolidone, vinylcaprolactam and dimethylaminoethyl (meth)acrylate monomer.
 15. Thedetergent composition of claim 9 wherein the aromatic monomer is styreneor methyl styrene.
 16. The detergent composition of claim 10 wherein theester monomer is vinyl acetate.
 17. The detergent composition of claim11 wherein the ester monomer derivative is selected from the groupconsisting of N-alkylaminoalkyl esters of acrylic or methacrylic acidand quaternized salts thereof.
 18. The detergent composition of claim 17wherein the N-alkylaininoalkyl ester of (meth)acrylic acid is di-(1-3carbon atom)alkylamino-(2-6 carbon atom)alkyl (meth)acrylate.
 19. Thedetergent composition of claim 17 wherein the N-alkylaminoalkyl ester of(meth)acrylic acid is dimethylaminoethyl (meth) acrylate ordiethylaminoethyl (meth)acrylate.
 20. The detergent composition of claim12 wherein the (meth)acrylic acid amide derivative is(3-(methacryloylamino)-propyl)-tri-methyl ammonium chloride.
 21. Thedetergent composition of claim 13 wherein the heterocyclic monomer isvinyl caprolactame.